In many applications, such as on board ships, there is a need for a lightweight, portable, engine driven pump unit. For example, such units are used as portable fire-fighting pumps or dewatering pumps. Present-day pump units of the indicated type generally utilize a two-stroke gasoline engine for driving the pump because this engine is light in weight. However, the use of gasoline as the fuel for the engine involves inherent safety problems because gasoline is so highly flammable.
Prior art engine-pump assemblies of the indicated type are disclosed in U.S. Pat. Nos. 4,643,652 and 4,690,613 wherein there is shown a unit wherein the pump is driven by a high speed, lightweight, gasoline engine of the two-cycle type used in outboard engines. The engine is arranged with a vertical crankshaft coupled to a vertical pumpshaft for driving the same.
It is an object of the present invention to provide an engine for use with a pump unit of the indicated type which is adapted to operate on a safe fuel such as kerosene based jet fuels like JP5 or diesel fuels such as DFM.
In accordance with this object, an engine that is designed to operate on gasoline is modified so as to operate with a kerosene based fuel JP5 as its fuel. One of the main difficulties to be overcome in operating a gasoline type engine of a fuel like JP5 is that JP5 has a much higher viscosity than gasoline, particularly at low temperatures. For example, at -50.degree. C. the viscosity of gasoline is 1.7 cs. while the viscosity of JP5 is 15.0 cs. Further, at 50.degree. C. the viscosity of gasoline is 0.5 cs. while the viscosity of JP5 is 1.1 cs.
In accordance with this object of the invention, in order to compensate for the higher viscosity of JP5, there is provided a novel carburetor means. More specifically, the idle and high speed fuel flow restrictions are made substantially larger than in a corresponding gasoline engine carburetor and the idle air bleed of a gasoline type carburetor is eliminated or plugged to thereby produce a much higher fuel flow at idle speed than with a comparable gasoline-type carburetor. This design compensates for the fact that JP5 does not burn as efficiently as gasoline especially at low throttle settings or engine speeds. In furtherence of this object of the invention, a fuel enrichment sub-system is provided. This system is constructed and arranged to bypass the high speed orifice and the idle tube orifice to compensate for the increased viscosity at extremely low temperatures. This enrichment system ensures that the system can flow enough fuel at low temperatures to maintain stable engine operation. A fuel enrichment needle valve controls the flow and is opened more as the temperature drops. The needle valve may be operated manually or controlled by a thermostat means to make the operation automatic. More specifically, the design is such that the fuel enrichment needle valve is fully open at the low point of temperature operation, i.e., -20.degree. F.,and gradually closes proportionately as the ambient operating temperature increases up to 60.degree. F. It will be apparent that in the fully-open position, the fuel flow is much richer than the other partially-open positions of the needle valve.
Another object of the invention is to provide a novel means for supplying a starting fuel of high volatility for use in starting the engine. While the engine will run well on JP5 once it is started and warmed up, there is a need for some starting assistance in order to start a cold engine. To this end, there is provided a novel starting fuel supply means comprising a sealed, pressurized cartridge containing a supply of the starting fuel, namely, propane. The cartridge is relatively small, structurally strong and explosion proof and is similar to the type of CO.sub.2 cartridges used for life vests. These cartridges have a burst pressure over 7000 PSI while propane has a room temperature vapor pressure of less than 150 PSI. Further, since only about 10-11 grams of propane are contained in each cartridge, they are very safe from a fire hazard point of view. It is noted that one cartridge provides all the propane required to start the engine at room temperature, although in cold conditions, more than one cartridge may be required.
A feature of the starting fuel supply means is that the flow of propane from a punctured cartridge to the engine carburetor is provided with an evaporator means, such evaporator means comprising an evaporator installed in the water pump priming bowl. This is done so that the heat from the sea water used to prime the pump can be utilized for the evaporation of propane in very cold conditions. It is noted that the boiling point of propane (-44.degree. F.) is so close to the low temperature requirement (-20.degree. F.) that the heat from the sea water (+28.degree. F.) is necessary to ensure consistent propane evaporation and reliable starting.
Another feature of the starting fuel supply means is the construction of the puncturing device which, in addition to puncturing the propane cartridge is provided with a built-in check valve function. To this end, when the cartridge is removed from the device, the check valve means closes and isolates the propane system from moisture and contaminants in the air, as well as preventing the escape of residual propane vapors into the atmosphere. Further, the sealing is enhanced by the provision of O-ring grooves in the puncture device that are twice as wide as normal to allow two O-rings of different compounds in each groove without the use of a back-up ring. This allows the puncture device to function properly from -44.degree. F. through 140.degree. F. This range of operation would not be possible with only one O-ring compound.
Another improvement in the starting fuel supply means is the provision of a propane regulator that has a shut-off feature that prevents the propane that has flowed through the puncture device and the evaporator from entering the engine until a manifold vacuum is present. The manifold vacuum produced as a result of pulling the engine start rope is sufficient to make the propane flow to the engine. Further, a prime button is provided on the regulator to bypass the shutoff function and for use in priming the engine with propane for quicker starts.
Another improvement in the starting fuel supply means is the provision of a storage rack for the cartridges that is mounted to the pump unit frame. This storage rack is designed to retain eight propane cartridges and also to protect these cartridges from heat and fire should the pump unit be engulfed in flames. To this end, the body of the cartridge tube is insulated while the end cap is exposed whereby not only is the maximum safe exposure time to fire greatly increased, but also the ultimate cartridge rupture is done in a controlled fashion. Further, since the body is cooler (because it is insulated from the fire) than the bottle tip, the bottle tip will rupture first in a prolonged immersion in fire. Accordingly, this produces a controlled plume of flame instead of an explosion and the cartridge remains in the storage rack to thereby eliminate possible shrapnel or explosion hazards.